Process for the welding of two polyamide parts

ABSTRACT

The invention relates to a process for the welding of two polyamide parts, both made of a polyamide composition comprising a polyamide and optionally additives, the polyamide of one part (part L) having a lower softening temperature than the polyamide of the other part (part H) and wherein the polyamide composition of part L comprises one or more viscosity increasing additives increasing the melt shear viscosity of the polyamide composition at least by 30% compared to melt shear viscosity of the polyamide (measured according to ISO 11443 (A1) standard at a shear rate of 100 s −1  in a capillary rheometer with I/d=30 mm/1 mm). The advantage is that a good weld strength is obtained and that parts with different properties can be combined. The invention further relates to polyamide welded objects obtainable by the process, like corrugated tubes, bellows, containers, fuel inlet systems, air inlet manifolds and airducts.

[0001] The invention relates to a process for the welding of twopolyamide parts, both made of a polyamide composition comprising apolyamide and optionally additives. The invention further relates topolyamide welded objects obtainable by the process, like corrugatedtubes, bellows, containers, fuel inlet systems, air inlet manifolds andairducts.

[0002] In WO 98/11164 it is described that two polyamide parts can bewelded together by vibration welding. In the two polyamide parts thepolyamide component is the same.

[0003] The inventors found that considerable practical advantages can berealized in a polyamide welded object comprising two polyamide partswelded together, both parts being made of a polyamide compositioncomprising a polyamide and optionally additives, the polyamide of onepart (part L) having a lower softening temperature than the polyamide ofthe other part (part H). With softening temperature is here andhereafter meant the melting temperature for crystalline polymers or theglass transition temperature for amorphous polymers. The advantage ofsuch a dissimilar polyamide welded object is that the properties of theobject as a whole can further be optimised by using in the objectdifferent polyamide materials at places where different materialproperties are required. For example, in automotive under the bonnetapplications, where both very high temperature resistance requirementsand high flexibility requirements exist, the object may be build up bywelding together a heat resistant polyamide, where heat resistance isrequired, and a flexible polyamide where flexibility, but no high heatresistance is required. The object performs better and/or can be madecheaper.

[0004] It is however generally considered that, in order to obtain aweld of sufficient strength, it is necessary that the polyamide in thetwo parts to be welded has to be the same. The main reasons for this arebelieved to be that dissimilar polyamides would show poor interactionand adhesion and that for vibration welding the higher melting part willnot or hardly melt and no sufficient weld strength is obtained.

[0005] It is the object of the invention to provide a process forwelding two polyamide parts, the polyamide of one part (part L) having alower softening temperature than the polyamide of the other part (partH). This object is according to the process of the invention achieved inthat the polyamide composition of part L comprises one or more viscosityincreasing additives increasing the melt shear viscosity of thepolyamide composition at least by 30% compared to the melt shearviscosity of the neat polyamide (measured according to ISO 11443 (A1)standard at a shear rate of 100 s⁻¹ in a capillary rheometer with I/d=30mm/1 mm). For the measurement of this increase in melt shear viscosity,the exact temperature of measurement is not very critical as long as themeasurement and comparison of the viscosity of both the polyamide andthe polyamide composition are done at the same temperature. Neverthelessit is preferred that the melt shear viscosity is measured at a normalstandard melt processing temperature of the polyamide, in particular forpolyamide-6 at 260° C. and for polyamide-6,6 at 280° C.

[0006] It was surprisingly found that with the process according to theinvention, acceptable weld strength could be obtained, as described inthe experiments. In view of obtaining a better weld strength in theprocess according to the invention, the melt shear viscosity at 100 s⁻¹of the polyamide composition of part L is increased at least 50%,preferably at least 70% and most preferably at least 100%.

[0007] It was found, in particular for polyamide-6 and polyamide-6,6,that good weld strength could be obtained if in the process according tothe invention, the melt shear viscosity of the polyamide composition ofpart L is at least 200 Pa.s, preferably at least 250 Pa.s, mostpreferably at least 300 Pa.s.

[0008] It was found that good weld strength could be obtained also byusing a high molecular weight polyamide in part L. A high molecularweight polyamide is considered a polyamide with a relative solutionviscosity of at least 2.4. The polyamide relative solution viscosity isdetermined from a solution of 1 gram/100 ml in 90% formic acid at 25° C.A relative solution viscosity of at least 2.4 is considered high formoulded parts, because these viscosities are normally used only forfiber, film or blow moulding. Put differently, good weld strengthresults are obtained by using a fiber, film or blow-moulding grade inthe moulded part L. Hence, in a preferred embodiment, the inventionrelates to a process for the welding of polyamide parts, with thepolyamide of one part (part L) having a lower softening temperature thanthe polyamide of the other part (part H), wherein the polyamidecomposition of part L comprises a high molecular weight polyamide and/orviscosity increasing additives and the polyamide composition of part Lhas a melt shear viscosity of at least 200 Pa.s, preferably at least 300Pa.s.

[0009] Preferably, the polyamide composition in part L comprisespolyamide having a relative solution viscosity between 2.0 and 4, inparticular between 2.4 and 4, and viscosity increasing additives. Arelative solution viscosity above 2 results in better weldability,whereas the relative solution viscosity preferably is less than 4because of processability reasons. A relative solution viscosity above2.4 gives better weld strength as explained above.

[0010] The combination of higher molecular weight polyamide withadditives has significant unexpected improvement, considered to be dueto be due to higher free end group concentration. Generally highermolecular weight polyamide requires less chain-stopper to obtain astable polymer and the intrinsic higher number of end-groups results inbetter interaction with other ingredients. Suitable polyamides have ingeneral 0.1 to 1 amine groups as end-groups per linear chain molecule;preferably the content of amine groups is at least 20 meq/kg and mostpreferably at least 40 meq/kg. The advantage of a higher amine groupcontent is a larger increase of the viscosity and more pronouncednon-Newtonian melt flow behaviour by reaction of anhydride groups in thebranching agent.

[0011] In principle, any combination of dissimilar polyamides can bechosen to combine intrinsically properties like high temperatureresistance and flexibility. Combinations of such polyamides are forexample polyamide-6/polyamide-6,6; polyamide-6/polyamide-4,6,polyamide-6,6/polyamide-4,6,-polyamide 4,6/semi-aromatic polyamide etc.Preferably, the polyamide of part H has a softening temperature above280° C. and the polyamide of part L has a softening temperature below270° C. Heat resistance often goes along with rigidity and lowflexibility, whereas high flexibility often goes along with low heatresistance. The combination of a part with a polyamide with softeningtemperature above 280° C. and a part with a the polyamide with asoftening temperature below 270° C. has the advantage that it combineshigh heat resistance and flexibility.

[0012] A preferred embodiment of a polyamide of part H with softeningtemperature above 280° C. is chosen from the group of polyamide-4,6 andsemi-aromatic (co-)polyamides like polyamide (6,6/6,T/6,1), polyamide(6,T/4,T). These polyamides have good heat stability and mechanicalproperties.

[0013] Most preferred is that the polyamide of part H is polyamide-4,6.Polyamide-4,6 is a polyamide well appreciated for its performance inengineering plastics in high temperature applications and polyamide-4,6is widely used polyamide, well available, moderately priced with goodflexibility properties.

[0014] The polyamide of part L with a softening point below 270° C. ischosen from aliphatic polyamides polyamide-6,6, polyamide-6,polyamide-4,10, polyamide-4,12 and any copolymers of these. Preferablythe polyamide is chosen from polyamide-6 or polyamide-6/6,6 copolymer.

[0015] The most preferred combination of a polyamide with softeningtemperature above 280° C. and a the polyamide with a softeningtemperature below 270° C. is the combination of polyamide-4,6 withpolyamide-6. The advantage of this combination is, that parts made ofthese polyamides show the best weld strength in welding of dissimilarpolyamide parts.

[0016] In another embodiment of the process according to the invention,the polyamide composition of part L comprises one or more viscosityincreasing additives chosen from the group of fibres, chain extenders,branching agents and nano-fillers. The advantage is that good weldingbehaviour can be obtained in combination with viscoelastic properties,which can be varied over a wide range.

[0017] The polyamide composition of part L comprises, as a viscosityincreasing additive, at least 10, preferably 20, more preferably 30 andmost preferably at least 40 w % fibres. The advantage is that betterwelding behaviour can be obtained in combination with good mechanicalstrength, which becomes even better with the higher fiber content. Manyfibres are suitable, like glass fibres, carbon fibres, whiskers etc.Preferably, the fiber is glass fiber, because glass fiber is very wellsuited to improve the welding strength, it is strong and it is cheap.

[0018] Preferably, the fiber has an aspect ratio L/d of at least 20. Theadvantage is that a fiber with an aspect ratio L/d of at least 20 has ahigher viscosity increase per unit mass than fibers with a lower aspectratio Lid.

[0019] In another embodiment of the process according to the invention,the polyamide composition of part L comprises, as a viscosity increasingadditive, a branching agent that reacts with the polyamide giving thepolyamide composition a non-Newtonian melt flow behaviour. Non-Newtonianmelt flow behaviour is here understood as the rheologic behaviour of amolten polymer composition wherein the melt shear viscosity of themolten polymer composition increases with decreasing shear rate.Preferably, the branching agent is combined with a polyamide withrelative solution viscosity of more than 2.4 and/or end groupconcentration of more than 20 meq/kg. Preferably such a branching agentis used in combination with glass fibres, yielding rigid products with avery good weld strength.

[0020] A suitable branching agent is an anhydride containing copolymer,preferably a copolymer of maleic anhydride and styrene. With anhydridecontaining polymer is understood a polymer containing anhydride groupsor other groups, like dicarboxylic acid groups, which groups can formanhydride groups under the polymer processing conditions.

[0021] Better weld strength is obtained when the branching agentcomprises a) a copolymer of at least an unsaturated dicarboxylic acid ora derivative thereof and a vinylaromatic monomer, preferably styrenemaleic anhydride copolymer (SMA), and b) a copolymer of acrylonitril anda vinylaromatic monomer, preferably styrene-acrylonitril copolymer (SMA)wherein (a) and (b) are miscible and the ratio (a)/(b) is between 1/3 to3/1. The advantage is that such a branching agent gives less gelformation and yields more homogeneous properties.

[0022] In an alternative embodiment of the process according to theinvention, the polyamide composition of part L comprises, as viscosityincreasing additive, a chain extender, such as carbonylbisimidazol orcarbonylbislactamate. The advantage is that due to in-situ reactionhigher molecular weights are achievable in the end-product than normallycan be used under standard processing conditions. Preferably the chainextender is carbonylbislactamate, more preferablycarbonylbiscaprolactamate. The advantage is that these chain extendersgive better properties in the end-product.

[0023] The invention in particular relates to a process according to theinvention, wherein the welding is done by laser welding, vibrationwelding or hot plate welding, preferably vibration welding. Theadvantages of the process according to the invention are present inparticular in case the welding is done by vibration welding.

[0024] The invention also relates to polyamide welded objects obtainableaccording to the process of the invention as described above. Suchwelded objects show a good weld strength. Preferably the weld strengthis at least 20 MPa, more preferably 40 MPa, most preferably 60 MPa.Preferably the weld strength is at least 30% of the bulk strength of thecomposition of Part L, more preferably at least 40% and most preferablyat least 50% of the bulk strength of the composition of Part L.

[0025] The invention further relates to polyamide welded objectcomprising two polyamide parts welded together both parts being made ofa polyamide composition comprising a polyamide and optionally additives,the polyamide of one part (part L) having a lower softening temperaturethan the polyamide of the other part (part H), wherein the polyamidecomposition of part L comprises a high molecular weight polyamide and/orviscosity increasing additives. The advantage of such welded object isthat it combines high temperature resistance and good flexibilitytogether with a good weld strength.

[0026] A preferred embodiment is constituted by a polyamide weldedobject wherein the polyamide composition of part L has a melt shearviscosity of at least 200 Pa.s, preferably at least 300 Pa.s. Such apolyamide welded object exhibits significant weld strength.

[0027] The invention also relates to the process for the manufacturingof a polyamide welded object wherein the welding is done by laserwelding, vibration welding or hot plate welding, preferably vibrationwelding.

[0028] The invention furthermore relates to corrugated tubes, bellows,containers, fuel inlet systems, air inlet manifolds, airductsmanufactured with to the process according to the invention.

[0029] The invention is further illustrated with the following examplesand comparative experiments.

[0030] Materials Used

[0031] SMA a styrene-maleic anhydride copolymer with a maleic anhydridecontent of 28 mass % (type Stapron® SZ28110, DSM, NL);

[0032] SAN a styrene-acrylonitril copolymer with a AN-content of 28 mass%, MFI (220° C., 10 kg) 50 g/10 min (DSM, NL);

[0033] LDPE a low-density polyethylene (type Lupolen® 1810H, BASF, DE);

[0034] PA-6-I polyamide-6, η_(rel)=2.2 (measured at 1 mass % in formicacid, 25°) (type Akulon® K122, DSM, NL); melt shear viscosity 140 Pa.sat 100 s⁻¹ and 260° C.

[0035] PA-6-II polyamide-6, η_(rel)=2.5 (measured at 1 mass % in formicacid, 25°) (type Akulon® C225, DSM, NL); melt shear viscosity 200 Pa.sat 100 s⁻¹ and 260° C.

[0036] PA-4,6 polyamide-4,6 (type Stanyl® TW 200; DSM, NL);

[0037] GF-I standard polyamide glass fiber used in polyamde-6 (type OCFCS 173X-10C; Owens Corning);

[0038] GF-II standard polyamide glass fiber used in polyamide-4,6 (typeOCF R 73WX1; Owens Corning).

[0039] Preparation of Branching Agent

[0040] A mixture of SMA/SAN/LDPE, with a mass ratio of 25/25150 wasextruded on an extruder type ZSK 57, with a temperature setting at 230°C. and a rotation speed of 200 rpm. The throughput was 110 kg/hour,controlled by the momentum at 85%. The mixture was easily extruded andcut into regular granules.

[0041] Preparation of Polyamide Composition

[0042] PA-6-1-GF

[0043] The 30 wt % glass fiber reinforced PA-6-1-GF was compounded fromPA-6-1 and GF-I in an double-screw extruder type ZSK 30 at a barreltemperature of 260° C., screw speed 250 rpm. The composition had a shearviscosity of 300 Pa.s at a shear rate of 100 s⁻¹ and 260° C.

[0044] PA-6-2-GF

[0045] The 30 wt % glass fiber reinforced PA-6-2-GF was compounded fromPA-6-2 and GF-I at the same conditions as PA-6-1-GF. The composition hada melt shear viscosity of 500 Pa.s at a shear rate of 100 s⁻¹ and 260°C.

[0046] PA-6-2-BA-GF

[0047] The composition of polyamide-6 modified with 2.7 mass % branchingagent and reinforced with 30 mass % glass fibre PA-6-2-BA-GF was made bycompounding PA-6-2, the branching agent SMA/SAN/LDPE (mass ratio25/25/50, described above), regular processing aids and stabilisers andglass fibre GF-1 on a ZSK30 twin-screw extruder. The temperature wascontrolled at 270° C., the throughput was about 10 kg/hour. Thecomposition had a shear viscosity of 1130 Pa.s at a shear rate of 100s⁻¹ and 260° C.

[0048] PA4,6-GF

[0049] The 30 wt % glass fiber reinforced PA4,6-GF was compounded fromPA-4,6 and GF-11 in a ZSK 25 extruder at a barrel temperature of 300°C., screw speed 275 rpm (throughput 20 Kg/h).

[0050] Melt Shear Viscosity Measurements

[0051] The melt shear viscosity of the polyamide and polyamidecompositions was measured according to ISO 11443 (A1) standard at ashear rate of 10 s⁻¹ in a capillary rheometer with I/d=30 mm/1 mm. Forpolyamide-6, the measurements were done at 260° C., for polyamide-6,6 at280° C.

[0052] Injection Moulding

[0053] For all the tested materials, plates of dimensions 120 mm×120mm×4 mm were injection moulded according to the following conditions

[0054] Injection Moulding of Polyamide-6 Materials

[0055] Injection moulding of the polyamide-6 materials PA-6-1, PA-6-2,PA-6-GF, PA-6-2-GF and PA-6-2-BAN-GF was performed on a KM 120injection-moulding machine with barrel temperature settings 230-260° C.and a mould temperature of 80° C.

[0056] Injection Moulding of Polyamide-4,6 Materials

[0057] Injection moulding of the polyamide-4,6 materials PA-4,6 andPA-4,6-GF was performed on a KM 120 injection-moulding machine withbarrel temperature settings 300-310° C. and a mould temperature of 120°C. was used.

[0058] Vibration Welding

[0059] The welding tests were done on a Bielomatik (Neuffen, Germany)vibration-welding machine, Type K3210. The welding parameters were asfollows: frequency: 240 Hz; amplitude: 0.9 mm; weld pressure: 2 Mpa;weld time: 4 s; hold time: 7 s. The process was time controlled to yieldan estimated weld depth of 1.8 mm. For each material-combination, 5weldings were executed.

[0060] For the purpose of the welding tests, the injection-moulded partswere cut in half along the 120 mm width. The butt-welded samples wereoriented in the tool such that the 120 mm×4 mm surface became the weldarea. Welding occurred on molded surfaces to more adequately representan industrial welding process. Vibration was parallel to the 120 mmplate width.

[0061] Tensile Testing

[0062] The butt-welded samples were cut into 10 mm wide tensilespecimens and loaded on a Zwick testing machine until fracture at acrosshead speed of 10 mm/min. The tensile strength was obtained by theforce at failure normalized by the weld area, being 4 mm×10 mm. Thestrain was measured with an extensiometer and established as themacroscopic strain at break; the real strain can be much higher in manycases. The values listed are averaged over five specimens. The relativeweld strength f*_(s)=σ_(weld)/σ_(bulk) is the ratio of the strength ofthe weld to the strength of the polyamide-6 composition used in thespecific combination.

EXAMPLES AND COMPARATIVE EXPERIMENT

[0063] Vibration welding according the above-described method was donefor the combinations of materials listed in Table I. Tensile tests wereperformed on these welded materials according above methods. The testresults are reported in Table I. TABLE I Heterogeneous weldings ofPolyamide-6 compositions to Polyamide-4,6-composition and tensile testresults ε at σ- Experiments/ σ-max max f_(r)* Examples Materials [MPa][%] σ_(weld)/σ_(bulk) Comparative PA-6-1 — No weld — Experiment A PA-4,6Example I PA-6-2 20 0.7 0.32 PA-4,6 Example II PA-6-1-GF 53 1.0 0.43PA-4,6-GF Example III PA-6-2-GF 60 1.3 0.48 PA-4,6-GF Example IVPA-6-2-BA-GF 63 1.5 0.58 PA-4,6-GF

1. Process for the manufacture of a polyamide welded object by laserwelding, vibration welding or hot plate welding, preferably by vibrationwelding of two polyamide parts, both made of a polyamide compositioncomprising a polyamide and optionally additives, the polyamide of onepart (part L) having a lower softening temperature than the polyamide ofthe other part (part H), characterized in that the polyamide compositionof part L comprises one or more viscosity increasing additivesincreasing the melt shear viscosity of the polyamide composition atleast by 30% compared to melt shear viscosity of the polyamide (measuredaccording to ISO 11443 (A1) standard at a shear rate of 100 s⁻¹ in acapillary rheometer with I/d=30 mm/1 mm).
 2. Process according to claim1, characterised in that the melt shear-viscosity of the polyamidecomposition of part L is increased at least 50%, preferably at least 70%and most preferably at least 100%.
 3. Process according to claim 1 or 2,characterised in that the melt shear viscosity of the polyamidecomposition of part L is at least 200 Pa.s, preferably at least 300Pa.s.
 4. Process for the manufacture of polyamide welded object by laserwelding, vibration welding or hot plate welding, preferably by vibrationwelding two polyamide parts made of a polyamide composition comprising apolyamide and optionally additives, the polyamide of one part (part L)having a lower softening temperature than the polyamide of the otherpart (part H), characterized in that the polyamide composition of part Lcomprises a high molecular weight polyamide and/or viscosity increasingadditives and the polyamide composition of part L has a melt shearviscosity of at least 200 Pa.s, preferably at least 300 Pa.s at 100 s⁻¹.5. Process according to anyone of claims 1 to 4, characterised in thatthe polyamide composition in part L comprises polyamide having arelative solution viscosity between 2.0 and 4, preferably between 2.4and 4 and viscosity increasing additives. The polyamide relativesolution viscosity is determined from a solution of 1 gram/100 ml in 90%formic acid at 25° C.
 6. Process according to any one of claims 1 to 5,characterised in that the polyamide of part H has a softeningtemperature above 280° C. and the polyamide of part L has a softeningtemperature below 270° C.
 7. Process according to claim 6, characterisedin that the polyamide of part H is chosen from the group ofpolyamide-4,6 and semi-aromatic (co-)polyamides like polyamide(6,6/6,T/6,1), polyamide (6,T/4,T),
 8. Process according to any one ofclaims 1 to 7, characterised in that the polyamide of part H ispolyamide-4,6 and the polyamide of part L is polyamide-6.
 9. Processaccording to any one of claims 1 to 8, characterised in that, thepolyamide composition of part L comprises one or more viscosityincreasing additive chosen from the group of fibers, chain extenders,branching agents and nano-fillers.
 10. Process according to claim 9,characterised in that, the polyamide composition of part L comprises, asa viscosity increasing additive, at least 10, preferably 20, morepreferably 30 and most preferably at least 40 w % fibers.
 11. Processaccording to claim 10, characterised in that the fiber is glass fiber.12. Process according to claim 10 or 11, characterised in that the fiberhas an aspect ratio L/d of at least
 20. 13. Process according to any oneof claims 1 to 8, characterised in that, the polyamide composition ofpart L comprises, as a viscosity increasing additive, a branching agentthat reacts with the polyamide giving the polyamide composition anon-Newtonian melt flow behaviour.
 14. Process according to claim 13,characterised in that the branching agent is an anhydride containingcopolymer, preferably a copolymer of maleic anhydride and styrene. 15.Process according to claim 13 or 14, characterised in that the branchingagent comprising a) a copolymer of at least an unsaturated dicarboxylicacid or a derivative thereof and a vinylaromatic monomer, preferablystyrene maleic anhydride copolymer (SMA), and b) a copolymer ofacrylonitril and a vinylaromatic monomer, preferablystyrene-acrylonitril copolymer (SMA) wherein (a) and (b) are miscibleand the ratio (a)/(b) is between 1/3 to 3/1.
 16. Process according toany one of claims 1 to 6, characterised in that, the polyamidecomposition of part L comprises, as a viscosity increasing additive, achain extender, preferably carbonylbislactamate.
 17. Polyamide weldedobjects obtainable according to the process of any one of claims 1 to16.
 18. Polyamide welded object comprising two polyamide parts laser,vibration or hot plate, preferably vibration welded together both partsbeing made of a polyamide composition comprising a polyamide andoptionally additives, the polyamide of one part (part L) having a lowersoftening temperature than the polyamide of the other part (part H),characterized in that the polyamide composition of part L comprises ahigh molecular weight polyamide and/or viscosity increasing additives.19. Polyamide welded object according to claim 17-18, characterised inthat the polyamide composition of part L has a melt shear viscosity ofat least 200 Pa.s, preferably at least 300 Pa.s at 100 s⁻¹. 20.Corrugated tubes, bellows, containers, fuel inlet systems, air inletmanifolds, air ducts manufactured with to the process according to anyone of claims 1 to 16.